In these days, various types of communication controllers are proposed in order to control communication of movable communication terminal devices such as mobile telephones. In such a communication controller, a communication system of global standard such as W-CDMA (Wide band Code Division Multiple Access) or UMTS (Universal Mobile Telecommunications System) is applied. According to the above communication system, a single frequency bandwidth is shared by multiple users by multiplexing codes, whereby the frequency efficiency is excellent and high-speed communication is made available in a flexible manner by selecting the code.
Such a conventional communication system is described in Non-Patent Document 1. The TNL (Transport Network Layer) used as an interface of the W-CDMA system is limited to ATM (Asynchronous Transfer Mode) in its original release, whereas Non-Patent Document 2 describes a technique applied as an option of the IP (Internet Protocol) Transport.
Generally, in the above communication system, a controller gives controls related to radio communication of a mobile telephone via a base transceiver station, so as to control the communication in a cell to be covered by the controller itself. ATM and IT transport have different control systems in information transmission in a network including, for example, between the controller and the base transceiver station. When the mobile telephone, which started radio communication in a cell controlled by a controller, moves to another cell while maintaining the communication, the mobile telephone has to be controlled by transmitting information between the controllers. Any one of ATM and IP Transport is employed for controlling the information transmission between the controllers.
That is to say, the controller that started the radio communication transmits information on the mobile telephone and for the communication control to the controller controlling the destination cell. In the destination cell, whether or not the start of communication is permitted is determined according to the congestion state. When the start of communication is permitted, the communication also continues subsequent to the movement. After that, the radio communication is continuously controlled by the controller of the source cell. The controller of the destination cell merely serves a role of relaying information between the controller of the source cell and the mobile telephone or the base transceiver station. This eliminates the takeover of control information or communication information from the controller of the source cell to the controller of the destination cell. This technique is referred to as subscriber line extension method.
In ATM Transport, ATM protocols are used for information transmission between the radio network controllers in the subscriber line extension method, whereas in IP Transport, IP protocols are used for information transmission.    Non-Patent Document 1: 3GPP Technical Standard TS21.101    Non-Patent Document 2: 3GPP Technical Report TR25.933